Question

Which term of the AP : 21, 42, 63, 84,... is 210

Answer 1

Given :

• First term ( a ) = 21

• Common difference ( d ) = 21

• Last term ( An ) = 210

To Find :

• Number of term 210

Solution :

★ An = a + ( n - 1 ) d

⇒ 210 = 21 + ( n - 1 ) × 21

⇒ 210 - 21 = ( n - 1 ) × 21

⇒ 189 = ( n - 1 ) × 21

⇒ 189 / 21 = n - 1

⇒ 9 = n - 1

⇒ n = 9 + 1

⇒ n = 10

210 is the 10th term of the A.P

Answer 2

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First term of the AP, a=21

Common difference d=21

'n'th term is 210

Then,

210=a+(n−1)d

210=21+(n−1)×21

210=21n

Therefore, n=10

Hence, 210 is 10th term of the series.